Rotating construction lasers are well known in the prior art. For example, in U.S. Pat. No. 7,370,427 a construction laser with at least one rotating laser beam defining a laser beam plane is described. The construction laser has a laser unit that is tiltable relative to a housing around at least one swiveling axis. The construction laser includes at least one level sensor which is sensitive to rotations around the swiveling axis for a highly precise orientation to the gravitational field. The device further includes one tilt sensor which is sensitive to rotations around the swiveling axis for direct measurement of an inclination angle relative to the gravitational field, with less resolution than the level sensor, but with a broader angular range that can be measured.
As a disadvantage of this embodiment, two sensors, a level sensor and a tilt sensor, are needed to measure tilt around one axis with an acceptable degree of accuracy. Furthermore, the laser beam unit periodically needs to return to its level position for recalibrating the tilt sensor.
WO 2008/052590 discloses a device for indicating a grade, for example in construction applications, using a laser beam. The laser beam is emitted from a laser unit to a desired direction having a grade angle with regard to the level angle. A level sensor is provided for adjusting the level angle and a grade sensor is provided for indicating a grade angle on the basis of the level angle from the level sensor. Thus, again two sensors are needed to correctly indicate the grade with respect to one axis of tilt.
According to U.S. Pat. No. 5,485,266, fixed tilt detectors are fixed in planes crossing perpendicularly to each other of a shaft center of a laser projector, and tilting tilt detectors are mounted on a plate which is tiltable with respect to the shaft center of the laser projector. The laser projector is level in such a manner that the fixed tilt detectors indicate horizontal direction. The tilting tilt detectors are aligned with the fixed tilt detectors and indicate a horizontal direction. Thus, a horizontal reference plane is obtained. The tilting tilt detectors are tilted with the fixed tilt detectors as a reference and the laser projector is leveled so that the tilting tilt detectors indicate horizontal direction. Thus, a reference plane tilted at an arbitrary angle is obtained.
This device also requires multiple tilt sensors.
In the prior art cited above, two tilt sensors are usually used for measuring the tilt of one axis of tilt of a rotating construction laser with high accuracy. One of these sensors is a level sensor which is of very high precision and very limited measurement range and typically used to calibrate the grade sensor or tilt sensor, which has a broader measurement range, but is less precise.
In U.S. Pat. No. 5,852,493 a self-aligning laser transmitter having a dual slope grade mechanism is disclosed. The laser transmitter includes a light source coupled to a frame which is suspended from a gimbal mechanism. The gimbal mechanism and the frame are coupled to a rotatable base. X and Y axes levelling devices are coupled to the gimbal mechanism and the frame to level the light source. A grade arm having two level sensors mounted at ninety degrees to one another is coupled to the frame. The grade arm is pivoted along the X or Y axes by a grade arm pivoting device. The X and Y axes leveling devices reposition the light source so that the level sensors are level thereby introducing a slope to the light source corresponding to the amount of pivot of the grade arm. The base may be rotated for a dual slope capability.
In this embodiment only two level sensors are used which, however, are mounted to the same grade arm. Consequently, upon a tilt of the grade arm caused by actuation of the X and Y axes levelling devices both level sensors are affected simultaneously. Hence, a precise calibration of the level sensors with regard to the X and Y axes is difficult. Typically a calibration with regard to either the X or the Y axis will be less precise than the other one.
In US 2008/0297921 a device for tilting the optical axis of a laser optical system is disclosed. Two tilt sensors are provided which are mounted on a common platform at an orientation of 90° with respect to each other. A gimbal mechanism supports tiltably the laser core module, comprising the laser light source and the beam-forming optical system of the laser. The gimbal mechanism also acts on the common platform of the two tilt sensors. Consequently, actuation of the X and Y axes levelling devices does affect both level sensors simultaneously also in this embodiment, again resulting in difficulties for a calibration of the level sensors with regard to tilting of the laser core module around the X and Y axes.